1. Field of the Invention
The present invention relates to a spark-ignition engine, and in particular, to a spark-ignition engine capable of reducing the content of hydrocarbon in exhaust gas.
2. Description of Related Art
A conventional spark-ignition engine includes a cylinder head-side squish surface provided on the outer periphery of a combustion chamber roof of a cylinder head, a piston head-side squish surface provided on the outer periphery of a piston head as opposed to the cylinder head-side squish surface, a combustion chamber recessed section recessed at the center of the combustion chamber roof of the cylinder head, an intake valve port provided on one opposed section of opposed sections of the combustion chamber recessed sections, an exhaust valve port provided on the other opposed section, and a spark-plug attachment hole facing the combustion chamber recessed section, in which the cylinder head-side squish surface and the piston head-side squish surface are upwardly inclined toward the combustion chamber recessed section, and in the vicinity of a compression top dead center, a squish flow is ejected from a squish area formed between the cylinder head-side squish surface and the piston head-side squish surface toward the center of the combustion chamber recessed section (refer to, for example, Japanese Utility Model JP 60-102428 U).
This kind of engine can advantageously cause disturbance of a fuel-air mixture in the combustion chamber recessed section by the squish flow, thereby increasing the propagation speed of flame generated by spark discharge of a spark plug to prevent engine knocking.
However, according to the conventional art, a spark discharge section at a tip of the spark plug is disposed at a position in the vicinity of a compression top dead center directly hit by a largest squish flow ejected from a squish area maximum-width section, which is disadvantageous.
Problem:
The content of hydrocarbon in exhaust gas increases.
Since the spark discharge section at the tip of the spark plug is disposed in the vicinity of a compression top dead center directly hit by the largest squish flow ejected from the squish area maximum-width section, a small fire source occurred in the spark discharge section immediately after ignition is blown out by the largest squish flow to prevent propagation of flame in the combustion chamber, increasing the content of hydrocarbon in exhaust gas due to incomplete combustion of fuel.